In this work, the possibility of application the device with a non-standard (side) piezoelectric sensor installation for rail condition monitoring is considered. The aim of this device application is reducing the risks of using single-strand flaw detectors on railway tracks with fixation system on the rail in the form of two rebords. Also, the application of this device allows you to obtain a new qualification criterion for the integrity of the rail, which is located in the railroad groundwork. This criterion is the presence of a signal from the opposite face of the rail head, which, in addition to the possible detection of a 30В.1-2 defect (DG) or 113 also allows you to record developed defects of the rail neck, passing into its head and implemented by sounding the rail head of the linear section of the track in the transverse direction (from the working to the non-working face). The study of round ultrasonic transducers of different frequencies was carried out. It has shown impossibility of using 10 MHz transducers. The results of statistical estimation of rail thickness and corresponding amplification levels are presented. The presence of statistically significant differences in the monitoring of different frequencies sensors and different sensors of the same frequency (which is relevant only for 5 MHz) was found. The difference between the maximum and minimum average in the test group of measured values of rail thickness was 0.06 mm, and between amplification levels — 17 dB.